Retrovirus vectors have received considerable attention as gene transfer vehicles for potential use in human therapy of single gene disorders, including Lesch-Nyhan syndrome. Lesch-Nyhan syndrome is caused by the deficiency of the enzyme hypoxanthine phosphoribosyltransferase (HPRT), and is characterized by behavioral alterations, including self-injurious behavior and mental retardation. The pattern of neurological abnormalities suggests potential involvement of the basal ganglia, where high levels of HPRT enzyme and mRNA have been detected in normal brain. Recombinant murine retroviruses have been developed as gene transfer vehicles to deliver functional gene products, such as HPRT, into cells that contain nonfunctional or deficient product. Recently, my laboratory isolated infectious molecular clones of a type D serogroup 2 simian retrovirus (SRV; D2/RHE/OR) and a variant virus found within Asian macaques; the infectious molecular clone of the variant (V1) appears to generate highly transmissible virus particles. These simian retroviruses exhibit broad tropism within the nonhuman primate, and have been found to productively infect the brain and nervous system. Sequence analysis of these molecular clones has allowed us to define the genetic structure of the SRV envelope (env) glycoprotein gene and to develop a structural model of simian retrovirus-cell interaction. The overall goal of this project is to develop the type D retrovirus as a gene transfer/therapy vehicle. We have now identified the V1 as the prime SRV gene transfer vehicle, and have identified important replication and morphogenesis signals, including the psi site essential for retrovirus packaging. We have also developed the packaging cell line vectors required for packaging of retrovirus particles. With these reagents, we are now in the position to assess the ability of the type D SRV gene transfer vehicle 640026ect and express reporter markers in the brain, and then utilize this vector as a potential gene therapy vehicle for the expression of HPRT in the Lesch-Nyhan syndrome nonhuman primate model.